Conventionally, image display devices each displaying different images for plural viewpoints to enable a viewer to perceive a stereoscopic image have been studied. This technology provides different images causing parallax for viewer's left and right eyes, and thereby realizes a stereoscopic image display device. Various methods to display stereoscopic images have ever been studied in order to achieve such the function concretely. Those methods can be classified broadly into methods to use eyeglasses and methods not to use eyeglasses. While the methods to use eyeglasses include an anaglyph method which uses different colors and a method to use polarization eyeglasses which uses polarization, those methods hardly avoid a bother in wearing eyeglasses essentially. Therefore, glassless methods wherein eyeglasses are not used have been studied briskly in recent years. The glassless methods include a parallax barrier method and a lenticular lens method.
First, a parallax barrier method will be described. FIG. 26 shows an optical model diagram illustrating a method of displaying stereoscopic images according to a parallax barrier method. As shown in FIG. 26, parallax barrier 105 is a barrier (a light-shielding plate) wherein plural aperture areas in a vertically-pinstriped shape, in other words, slits 105a are formed thereon. Display panel 102 is arranged in the vicinity of one surface of parallax barrier 105. In display panel 102, there are arranged pixels for a right eye 123 and pixels for a left eye 124 along a direction perpendicular to the elongated direction of slits 105a. There is arranged light source 108 in the vicinity of the other surface of parallax barrier 105, in other words, opposite from display panel 102.
Light emitted from light source 108 is partially shielded by parallax barrier 105. On the other hand, as for light which has passed through slits 105a without being shielded by parallax barrier 105, a part of the light passes thorough a pixel for a right eye 123 to become light flux 181 and another part of the light passes thorough a pixel for a left eye 124 to become light flux 182. In this situation, a viewer's position where the viewer can perceive a stereoscopic image is defined by a positional relationship between parallax barrier 105 and the pixels. That is, it is required that right eye 141 of viewer 104 is located in an area where all the light fluxes 181 corresponding to plural pixels for right eye 123 pass through and left eye 142 of viewer 104 is located in an area where all the light fluxes 182 pass through. This corresponds to the situation that middle point 143 of the positions of right eye 141 and left eye 142 of the viewer is located in the stereoscopic perceptive range 107 shown as the tetragon in FIG. 26.
Among line segments extending in the arrangement direction of pixels for a right eye 123 and pixels for a left eye 124 in the stereoscopic perceptive range 107, a line segment passing intersection 107a of diagonal lines of stereoscopic perspective range 107 is the longest. Therefore, a tolerance for the displacement of a viewer in the left and right directions becomes the maximum under the condition that middle point 143 is located at intersection 107a, and such the condition is the most preferable as a viewing point. Accordingly, in the stereoscopic image display method, it is recommended that viewers perform viewing at best viewing distance OD, assuming the distance between intersection 107a and display panel 102 as the best viewing distance OD. Herein, a virtual plane on which a distance from display panel 102 keeps best viewing distance OD in the stereoscopic perceptive region 107 is defined as best viewing surface 107h. This structure allows light from pixels for a right eye 123 and light from pixels for a left eye 124 reach right eye 141 and left eye 142 of a viewer, respectively, which enables the viewer to perceive an image displayed on display panel 102 as a stereoscopic image.
At the beginning of devising the above-described parallax barrier method, a parallax barrier was arranged at a position between the pixels and the eyes, which caused a problem that the parallax barrier obstructed the view and provided low visibility. However, the recent realization of liquid crystal displays allowed parallax barrier 105 to be arranged behind display panel 102 as shown in FIG. 26, which solved the problem of visibility. Therefore, stereoscopic image display devices using the parallax barrier method are currently studied briskly and stereoscopic image display devices to which the parallax barrier method is applied are actually in the market as products.
Next, a lenticular lens method will be described. FIG. 27 is a perspective view illustrating a lenticular lens. FIG. 28 is an optical model diagram illustrating a method of displaying stereoscopic images by using the lenticular lens method. FIG. 29 is a perspective view illustrating a stereoscopic display device. As shown in FIG. 27, lenticular lens 121 has a flat plane on one surface, and plural projecting sections each having a semi-cylindrical shape (cylindrical lenses 122) formed on the other surface, where the plural projecting sections extend in one direction and are arranged with their elongated direction being parallel with each other.
As shown in FIGS. 28 and 29, a stereoscopic image display device using the lenticular lens method includes lenticular lens 121, display panel 102 and light source 108 arranged in order from a viewer, and pixels of display panel 102 are placed on a focus plane of lenticular lens 121. On display panel 102, pixels 123 for right eye 141 and pixels 142 for left eye 142 are arrayed one after the other. Under the situation, groups each composed of neighboring pixels 123 and 124 correspond to cylindrical lenses (projection sections) 122 of lenticular lens 121, respectively. This structure makes cylindrical lenses (projection sections) 122 of lenticular lens 121 separate light which has been emitted from light source 108 and passed through respective pixels in directions toward the right and left eyes by and makes the left and right eyes perceive different images, which enables the viewer to perceive a stereoscopic image.
In construct to the above-described parallax barrier method which is a method to “block” unwanted light by using a barrier, the lenticular lens method is a method to change the way light travels, and does not theoretically cause a deterioration of brightness of the display panel coming from arrangement of a lenticular lens. Therefore, this method is regarded as very likely to be applied to mobile devices wherein bright display and low power consumption are valued especially.
The stereoscopic image display device has five viewpoints in the horizontal direction. A viewer can observe five different images on the device by changing the viewing angle in the horizontal direction.
As an example of an image display device which can display different images for plural viewpoints, a display for simultaneously displaying multiple images has been disclosed in Japanese Published Unexamined Patent Application (JP-A) No. H06-332354. The display disclosed in JP-A No. H06-332354 simultaneously displays different planer images in the same condition in each of the viewing directions by utilizing an image distributing function coming from a lenticular lens, whereby making it possible for a plural different viewers to simultaneously observe, on a single display, different planer images from different directions, respectively.
In order to achieve the above-described image display device, liquid crystal display devices are generally used in most cases. Herein, there is cited a structural example of a general liquid crystal display device disclosed in Japanese Examined Patent application (JP-B) No. 4089843. FIG. 30A is a sectional view showing a sectional structure disclosed in JP-B No. 4089843. Each of FIGS. 30B and 30C is a sectional view showing an example of a sectional structure which is assumed based on the structure of FIG. 30A.
FIG. 30A shows a structure that transparent substrate (at the side of TFT (Thin Film Transistor)) 202 and transparent substrate (at the side of a common electrode) 203 are arranged to face each other. On transparent substrate (at the side of TFT) 202, there are formed gate insulator 208, drain lines (signal lines) 207, organic insulator 213 and pixel electrodes 205. On transparent substrate (at the side of the common electrode) 203, there are formed color filters r, g, and b, black matrix 211 and common electrode 210. While drain lines 207 and black matrix 211 are almost the same in width in this structure, there can be considered the structure that drain lines 207 are larger than black matrix 211 in width as shown in FIG. 30B. Alternatively, there can be considered the structure that black matrix 211 is larger than drain line 207 in width as shown in FIG. 30C.
Next, there is cited JP-A No. 2009-98311 as a known art providing display of stereoscopic view with enhanced image quality. FIG. 31A shows a sectional view illustrating a sectional structure of JP-A No. 2009-98311. FIG. 31B shows a plan view showing a pixel structure of JP-A No. 2009-98311.
As shown in FIG. 31A, the sectional structure of a display device of JP-A No. 2009-98311 has a structure that lenticular lens 303 is arranged on display panel 302 and display panel 302 is formed by layering TFT substrate 302a and counter substrate 302b with liquid crystal 305 put between them.
As shown in FIG. 31B, one of features of pixels of JP-A No. 2009-98311 is that data line D (equivalent to drain line (signal line) 7 of JP-B No. 4089843) are inclined at angle with the Y-axis. Under the condition that there is a structural element, such as lenticular lens 303, having a function to distribute optical paths of light emitted from display panel 302, a viewer observes brightness of various parts of an aperture area of a pixel along the X-axis direction on the sheet of FIG. 31B. If a part of the aperture area of a pixel has a brightness which is significantly different from the other parts, the viewer perceives the difference in brightness, which means that the viewer observes a deteriorated view. However, as for a pixel shown in FIG. 31B, the viewer does not perceive the difference in brightness even when moving the viewpoint along the X axis, under the condition that the relationship h=h1+h2 holds, where h represents length of a part where light passes through out of line B-B running in the Y-axis direction and h1 and h2 represent lengths of parts where light passes through out of line A-A running in the Y-axis direction. Thereby, the viewer can view an image stereoscopically displayed in an excellent display condition.
However, the above conventional arts have problems which will be described below.
Problems which can be caused when the structures of the conventional arts are applied to a stereoscopic image display device will be described, with reference to FIGS. 32A to 32C. The upper parts of FIGS. 32A to 32C are plan views each showing the condition that black matrix 211 and drain line 207 are overlapped with each other between neighboring pixels, viewed from the normal direction of the transparent substrates. The lower parts of FIGS. 32A to 32C are diagrams each showing brightness (light amount) at respective positions on pixels. Transparent substrate (at the side of TFT) 202 and transparent substrate (at the common electrode) 203 are joined together with an unillustrated spacer being arranged between them. In this situation, they can be joined together with displacement depending on accuracy of a machine.
Referring with FIG. 32A, there will be described the situation that, when drain line 207 and black matrix 211 both working as a light-shielding member are almost the same in width, the displacement between the joined transparent substrates has been caused. In this situation, it is assumed that transparent substrate (at the side of the counter electrode) 203 has shifted to the right-hand side in the FIG. 32A under the condition that the position of transparent substrate (at the side of TFT) 202 has been fixed. Symbols h and h1 through h3 represent heights at respective positions of aperture areas (which will be called as aperture-area heights hereinafter). Symbols Wb1 and Wb2 represent the sizes of widths of light-shielding sections which are located between pixels and are areas where light does not pass through (which will be called as light-shielding widths). Symbols d1 and d2 represent direction components of Wb1 and Wb2 measured in the height direction of the aperture areas and are defined by the following expressions, where θ is the angle of the light-shielding section.d1=Wb1/sin θd2=Wb2/sin θ
In the situation that there is no displacement (the left part of FIG. 32A), the relationship of the aperture-area heights h=h1+h2 holds. Therefore, in the graph with position on pixels as the horizontal axis and brightness as the vertical axis, the brightness keeps the almost constant value L. On the other hand, in the situation that there is the displacement (the right part of FIG. 32A), the edge part of drain line 207 is exposed because of the displacement of black matrix 211 in the right, which enlarges the light-shielding width from Wb1 to Wb2 (>Wb1). This situation also enlarges the height-direction component d1 to d2 (>d1). In contrast, aperture-area height h2 is decreased to h3 (<h2) because the displacement enlarges height-direction component d1 to d2. Therefore, assuming the reduction of brightness depending on the decrease of the aperture-area heights as reduction amount 1, the vicinity of the light-shielding member becomes dark by the reduction amount 1. In other words, when the displacement between the joined transparent substrates has been caused in the structure of FIG. 32A, a part with poor brightness appears at a certain position on a pixel, which deteriorates quality of images.
Referring with FIG. 32B, there will be described the situation that the displacement between the joined transparent substrate has been caused, in the structure that black matrix 211 is larger than drain line 207 in width. Similarly to FIG. 32A, it is assumed that the transparent substrate (at the side of the counter electrode) 203 has shifted to the right-hand side under the condition that the position of transparent substrate (at the side of the TFT) 202 is fixed. Symbols h, h1 and h2 represent aperture-area heights. Symbols Wb represents the light-shielding width. Symbol d represents a direction component of Wb measured in the height direction of the aperture areas and is defined by the following expression, where θ is the angle of the light-shielding section.d=Wb/sin θ
In the situation that there is no displacement (the left part of FIG. 32B), the relationship of the aperture-area heights h=h1+h2 holds. Therefore, in the graph with position on pixels as the horizontal axis and brightness as the vertical axis, the brightness keeps the almost constant value L. On the other hand, in the situation that there is the displacement (the right part of FIG. 32B), though black matrix 211 is displaced in the right direction, drain line 207 is hidden behind black matrix 211 with avoiding the situation that drain line 207 is exposed as shown in FIG. 32A because drain line 207 is thinner than black matrix 211. Therefore, light-shielding width Wb does not change. Accordingly, the value of d also does not change, which avoids that the relationship h=h1+h2 breaks down because of the displacement between the joined transparent substrate. Therefore, even when the displacement between the joined transparent substrates has been caused, it does not deteriorate image quality.
However, the structure shown in FIG. 32B requires making black matrix 211 larger than drain line 207 in width, which makes the light-shielding width wider. Hereinafter, a problem which can be caused when the light-shielding width becomes wide will be described with reference to FIG. 33. It is assumed that the light-shielding width enlarged from Wb1 to Wb2 (Wb1<Wb2) as shown in FIG. 33. In order to make the aperture-area heights of the pixels at the left-hand side and the right-hand side equal to each other, the displacement amount between neighboring pixels in the Y-axis direction is required to increase from e1 to e2 (e1<e2). In other words, when the light-shielding width becomes larger with keeping the same resolution (which corresponds to the case that the distance between pixels is kept to be constant), the aperture-area height decreases from h1 to h2 (h1>h2), which causes another problem that the aperture areas become small.
Referring with FIG. 32C, there will be described the situation that the displacement between the joined transparent substrate has been caused, in the structure that drain line 207 is larger than black matrix 211 in width. Similarly to FIG. 32A, it is assumed that transparent substrate (at the side of the counter electrode) 203 has shifted to the right-hand side under the condition that the position of transparent substrate (at the side of the TFT) 202 is fixed. Symbols h, h1 and h2 represent aperture-area heights. Symbols Wb represents the light-shielding width. Symbol d represents a direction component of Wb measured in the height direction of the aperture areas and is given by the following expressions, where θ is the angle of the light-shielding section.d=Wb/sin θ
In the situation that there is no displacement (the left part of FIG. 32C), the relationship of the aperture-area heights h=h1+h2 holds. Therefore, in the graph with position on pixels as the horizontal axis and brightness as the vertical axis, the brightness keeps the almost constant value L. On the other hand, in the situation that there is the displacement (the right part of FIG. 32C), though black matrix 211 is displaced in the right direction, light-shielding width Wb is defined by drain line 207 regardless of the position of black matrix 211 because black matrix 211 is thinner than drain line 207. Accordingly, the value of d also does not change, which avoids that the relationship h=h1+h2 breaks down because of the displacement between the joined transparent substrate. Therefore, even when the displacement between the joined transparent substrates has been caused, it does not deteriorate image quality.
However, the structure shown in FIG. 32C requires making drain line 207 larger than black matrix 211 in width, which makes the light-shielding width wider. Similarly to the case of FIG. 32B, it causes the problem that the aperture areas become small.
While the above has described situation that drain line 207 and black matrix 211 form a light-shielding section, the above-described problems can also be caused under the situation that a light-shielding section is composed of arbitrary light-shielding members formed on the two transparent substrates.
Accordingly, when a general liquid crystal display device is applied to a display device capable of displaying stereoscopic images, the displacement between the joined transparent substrates can cause the problem that image quality is deteriorated because of the difference in brightness depending on a position on pixels, and enlarging the width of one of the light-shielding members can cause the problem that the opening ratio of the display section is decreased because of enlargement of the light-shielding section.